TMS27C240 262144 BY 16BIT UV ERASABLE

TMS27PC240 262144 BY 16BIT

PROGRAMMABLE READONLY MEMORIES

SMLS240D− NOVEMBER 1990 − REVISED SEPTEMBER 1997

4

POST OFFICE BOX 1443

latchup immunity

Latchup immunity on the TMS27C240 and TMS27PC240 is a minimum of 250 mA on all inputs and outputs.

This feature provides latchup immunity beyond any potential transients at the P.C. board level when the devices

are interfaced to industry-standard TTL or MOS logic devices. Input-output layout approach controls latchup

without compromising performance or packing density.

power down

100

µA by applying a high CMOS input on E. In this mode all outputs are in the high-impedance state.

erasure ( TMS27C240)

Before programming, the TMS27C240 is erased by exposing the chip through the transparent lid to a high

intensity ultraviolet light (wavelength 2537 Å). The recommended minimum exposure dose (UV intensity

×

exposure time) is 15-W

should be located about 2.5 cm above the chip during erasure. After erasure, all bits are in the high state. It

should be noted that normal ambient light contains the correct wavelength for erasure. Therefore, when using

the TMS27C240, the window should be covered with an opaque label.

initializing ( TMS27PC240)

The one-time programmable TMS27PC240 PROM is provided with all bits in the logic high state, then logic lows

are programmed into the desired locations. Logic lows programmed into an OTP PROM cannot be erased.

SNAP! Pulse programming

The TMS27C240 and TMS27PC240 are programmed by using the SNAP! Pulse programming algorithm. The

programming sequence is shown in the SNAP! Pulse programming flow chart, shown in Figure 1.

is presented in parallel (eight bits) on pins DQ0 through DQ15. Once addresses and data are stable, the

programmed only once before going to interactive mode.

verification and programming is performed up to a maximum of 10 times. When the device is fully programmed,

program inhibit

Programming can be inhibited by maintaining a high level input on the E and G pins.

program verify